The conductor is hollow, and liquid helium flows through it during operation. Between the cryogenic envelope and the conductor, there is a channel, through which liquid or gaseous helium also flows as a return line.
The cryogenic envelope consists of several corrugated metal tubes, arranged a certain distance from each other, between which a vacuum is present as well as so-called “superinsulation”.
A cable of this type can be produced in lengths of up to 200 m on a continuous production basis. The maximum transmission-line power of a system consisting of two of these types of single-conductor cables is 5 GW.
A superconducting cable in which a plurality of tapes, consisting of so-called 2nd-generation superconducting material, are wrapped around a support tube, through which liquid nitrogen flows, is known from spring 1999 edition of the Epri Journal. These modern superconductors consist of flexible metal tape, onto which an yttrium-barium-copper oxide compound has been applied.
A corrugated metal tube is provided over the superconducting tapes. Several layers of thermal insulation are then wrapped around the corrugated metal tube. The thermal insulation is surrounded by a second corrugated metal tube, and a spacer of Teflon is also provided on the thermal insulation. A solid dielectric and an external electrical shield are installed around the second corrugated metal tube.
Common to both types of cable is that, when the cable is in the operating state and the superconductor and the cable elements surrounding it are at the temperature of the liquid helium or of the liquid nitrogen, they become shorter than the external cable elements, which are at ambient temperature. To prevent this decrease in length, fittings are provided at both ends of the cable to connect the individual cable elements nonpositively to each other and thus to prevent the inner cable elements from becoming shorter than the outer cable elements.
Proceeding from this state of the art, the task of the present invention consists in providing a process for the production of superconducting cable, according to which it is guaranteed during the production process itself that the cable core will not contract as a result of a drop in temperature and become shorter than the outer cable elements, which are at ambient temperature.